The four types of brahmacari that I know are: naisthika-brahmacari, brahma-brahmacari, prajapatya-brahmacari and savitra-brahmacari (I'm guessing that savitra-brahmacari is another name for gayatra-brahmacari which you mentioned).
Out of these, the last three are upakurvana-brahmacaries, which means that the brahmacari can marry later, after the brahmacari period is over.
"There are four types of brahmacaris. The first is called savitra, which refers to a brahmacari who, after initiation and the sacred thread ceremony, must observe at least three days of celibacy. The next is called prajapatya, which refers to a brahmacari who strictly observes celibacy for at least one year after initiation. The next is called brahma-brahmacari, which refers to a brahmacari who observes celibacy from the time of initiation up to the time of the completion of his study of the Vedic literature. The next stage is called naisthika, which refers to a brahmacari who is celibate throughout his whole life. Out of these, the first three are upakurvana, which means that the brahmacari can marry later, after the brahmacari period is over. The naisthika-brahmacari, however, is completely reluctant to have any sex life."
The most known and prominent naisthika-brahmacaris in Vedic tradition are; the four Kumaras and Narada Muni.